Conventionally diacetals such as 1,3:2,4-bis-O-(p-methylbenzylidene)-D-sorbitol and the like have been incorporated as a nucleating agent into polyolefin resins to improve the optical properties of the polyolefin resins such as transparency and gloss, their mechanical properties such as rigidity and their thermal properties (e.g. Japanese Unexamined Patent Publication No. 117044/1978).
However, the above-mentioned diacetal nucleating agent has posed problems of frequently developing fish eyes in the obtained molded products and coloring the molded products yellow. While polyolefin resins containing said diacetal nucleating agent are considerably improved in the above optical, mechanical and thermal properties compared with polyolefin resins free of the diacetal nucleating agent, there is a need for further improvements in optical, mechanical and thermal properties in view of the current growing demand for high qualities.
From the viewpoint of methods for molding polyolefin resins, problems are raised. That is, in high temperature melting molding methods, molded products tend to become yellowish, whereas in low temperature melting molding methods, fish eyes are easily formed due to a non-dispersed nucleating agent although the coloration of the molded products are suppressed.
An object of the present invention is to provide a nucleating agent which is capable of preventing the occurrence of the above-mentioned fish eyes and coloration and capable of increasing the molding speed and further improving the optical, mechanical and thermal properties of polyolefin resins, as well as a polyolefin resin composition and molded products containing such nucleating agent.
Another object of the invention is to provide a method for molding polyolefin resins substantially free of the foregoing prior art problems.